The present invention relates to an integrated front projection display system. In particular, the present invention relates to a low-profile integrated front projection system that coordinates specialized projection optics and an integral screen optimized to work in conjunction with the optics to create the best viewing performance and produce the necessary keystone correction.
Electronic or video display systems are devices capable of presenting video or electronically generated images. Whether for use in home-entertainment, advertising, videoconferencing, computing, data-conferencing or group presentations, the demand exists for an appropriate video display device.
Image quality remains a very important factor in choosing a video display device. However, as the need increases for display devices offering a larger picture, factors such as cost and device size and weight are becoming vital considerations. Larger display systems are preferable for group or interactive presentations. The size of the display system cabinet has proven an important factor, particularly for home or office use, where space to place a large housing or cabinet may not be available. Weight of the display system also is an important consideration, especially for portable or wall-mounted presentations.
Currently, the most common video display device is the typical CRT monitor, usually recognized as a television set. CRT devices are relatively inexpensive for applications requiring small to medium size images (image size traditionally is measured along the diagonal dimension of a rectangular screen). However, as image size increases, the massive proportions and weight of large CRT monitors become cumbersome and severely restrict the use and placement of the monitors. Also, screen curvature issues appear as the screen size increases. Finally, large CRT monitors consume a substantial amount of electrical power and produce electromagnetic radiation.
One alternative to conventional CRT monitors is rear projection television. Rear projection television generally comprises a projection mechanism or engine contained within a large housing for projection up on the rear of a screen. Back-projection screens are designed so that the projection mechanism and the viewer are on opposite sides of the screen. The screen has light transmitting properties to direct the transmitted image to the, viewer.
By their very nature, rear projection systems require space behind the screen to accommodate the projection volume needed for expansion of the image beam. As background and ambient reflected light may seriously degrade a rear projected image, a housing or cabinet generally encloses the projection volume. The housing may contain a mirror or mirrors so as to fold the optical path and reduce the depth of the housing. The need for xe2x80x9cbehind-the-screenxe2x80x9d space precludes the placing of a rear projection display on a wall.
A new category of video presentation systems includes so-called thin Plasma displays. Much attention has been given to the ability of plasma displays to provide a relatively thin (about 75-100 nun) cabinet, which may be placed on a wall as a picture display in an integrated compact package. However, at the present time, plasma displays 3 are costly and suffer from the disadvantages of low intensity (approx. 200-400 cd/m2 range) and difficulty in making repairs. Plasma display panels are heavy (xcx9c80-100 lbs., xcx9c36-45 kg.), and walls on which they are placed may require structural strengthening.
A traditional type of video presentation device that has not received the same degree of attention for newer applications is front-projection systems. A front-projection system is one that has the projection mechanism and the viewer are on the same side of the screen. Front projection systems present many different optical and arrangement challenges not present in rear projection systems, as the image is reflected back to the audience, rather than transmitted. An example of front projection systems is the use of portable front projectors and a front projection screen, for use in meeting room settings or in locations such as an airplane cabin.
One of the advantages of front projectors is the size of the projection engine. Electronic front projectors traditionally have been designed for the smallest possible xe2x80x9cfootprintxe2x80x9d, a term used to describe the area occupied on a table or bench, by the projector. Portable front projectors have been devised having a weight of about 10-20 lbs. (xcx9c4.5-9 kg.).
Nevertheless, front projection systems have traditionally not been considered attractive for newer interactive applications because of factors such as blocking of the image by the projector or the presenter, poor image brightness, image distortion and setup 2o difficulties.
Traditional electronic front projectors typically require a room that may afford the projection volume necessary for image expansion without any physical obstructions. Although images may be projected upon a large clear flat surface, such as a wall, better image quality is achieved by the use of a separate screen. FIGS. 1 and 2 illustrate a traditional front projection system. A projector 10 is placed on a table or other elevated surface to project an image upon a screen or projection surface 20. Those familiar with the use of electronic projectors will appreciate that tilting the projector below the normal axis of the screen produces a shape distortion of the image, known as a keystone effect. Most new electronic projectors offer a limited degree of keystone correction. However, as may be appreciated in FIG. 2, the placement of the projector may still interfere with the line of sight of the audience.
Of greater significance is the fact that to achieve a suitable image size, and also due to focus limitations, the projector 10 requires a certain xe2x80x9cprojection zonexe2x80x9d in front of the screen 20. Table A lists the published specifications for some common electronic projectors currently in the market.
Throw distance is defined as the distance from the projection lens to the projection screen. Throw ratio usually is defined as the ratio of throw distance to screen diagonal. The shortest throw distance available for the listed projectors is one meter. To achieve a larger image, between 40 to 60 inches (xcx9c1 to 1.5 meters), most projectors must be positioned even farther away, at least 8 to 12 feet (approximately 2.5 to 3.7 meters) away from the wall or screen.
The existence of this xe2x80x9cprojection zonexe2x80x9d in front of the screen prevents the viewer from interacting closely with the projected image. If the presenter, for example, wishes to approach the image, the presenter will block the projection and cast a shadow on the screen.
Traditional integrated projectors require optical adjustment, such as focusing every time the projector is repositioned, as well as mechanical adjustment, such as raising of front support feet. Electronic connections, such as those to a laptop computer, generally are made directly to the projector, thus necessitating that the projector be readily accessible to the presenter or that the presenter runs the necessary wiring in advance.
Another problem with front projectors is the interference by ambient light. In a traditional front projector a significant portion of the projected light is scattered and is not reflected back to the audience. The loss of the light results in diminished image brightness. Accordingly, a highly reflective screen is desirable. However, the more reflective the screen, the larger the possible degradation of the projected image by ambient light sources. The present solution, when viewing high quality projection systems such as 35 mm photographic color slide presentation systems, is to attempt to extinguish an ambient lights. In some very critical viewing situations, an attempt has been made even to control the re-reflection of light originating from the projector itself.
Some screen designers have attempted to address the ambient light problem with xe2x80x9cmono-directional reflectionxe2x80x9d screens, that is, a projection screen attempts to absorb fight not originating from the projector, while maximizing the reflection of incident light originating from the direction of the projector. Nevertheless, since portable projectors are, in fact, portable and are used at various throw distances and projection angles, it has proven very difficult to optimize a screen for all possible projector positions and optical characteristics.
An alternative is to design a dedicated projection facility. Such a design necessitates a dedicated conference room, in which the projector and screen position, as well as the projector""s optical characteristics, are rigorously controlled and calibrated. Structural elements may be used to suspend the selected projector from the ceiling. Once calibrated, such system would be permanently stationed. Such a facility may suffer from high costs and lack of portability.
Another issue that prevents optimal performance by front projectors is the keystone effect. If projectors are placed off-center from the screen, keystoning will occur. Keystoning is a particular image distortion where the projection of a rectangular or square image results in a screen image that resembles a keystone, that is a quadrilateral having parallel upper and lower sides, but said sides being of different lengths.
Methods for the reduction of keystoning again are dependent upon the position of the projector with respect to the screen. Keystone correction may be achieved by optical and by electronic methods. For large keystone correction in LCD imagers, optical methods are presently preferable, as electronic methods may suffer from pixelation distortion, as pixels become misaligned. Presently, to the applicants"" knowledge, the available optical keystone correction in commercially available portable electronic front projectors is between 10xc2x0 to 20xc2x0.
The need remains for a large screen video presentation system that offers efficient space utilization, lower weight and attractive pricing. Such a system should preferably yield bright, high-quality images in room light conditions.
An embodiment of the present invention comprises a front projection display system that integrates an optical engine, having control and power supply electronics, and a dedicated projection screen to provide a compact video display device. The projection engine is coupled to a high gain projection screen, having an optimized reflection pattern to give optimum optical performance in ambient light and viewing angle sensitive environments. Components of the projection engine are modularly placed in a retractable arm, pivotally connected to the screen. The arm offers precise registration to the screen apparatus and thus repeatably precisely aligns optically and mechanically to the screen. The projection wall system has an open projection position and a closed storage position. The architecture is very flat and light, having depth of less than three inches (xe2x88x927.5 cm.) and a weight of less than 25 pounds (11 kilograms). Use of a radically offset projection head having matching keystone correction features allows the arm to protrude above the head of the presenter and offer a sharp and unobtrusive projection zone.
An exemplary integrated front projection display in accordance with the present invention includes a front projection screen, a pivoting arm coupled to the flat projection screen, the arm having a storage position and a projection positionxe2x80x94and a front projection head coupled to the arm. When the arm is in the projection position, the front projection head is at a predetermined position with respect to the front projection screen.
The projection head includes projection optics having mechanical off-axis keystone correction compensation greater than or approximately equal to 22xc2x0, a throw distance of at most 800 mm, a throw-to-screen diagonal ratio of at most 1.
The front projection screen may have a vertically graduated reflection distribution, wherein light rays emanating from the projection position generally are reflected by the projection screen in a preselected direction, normal to the vertical axis of the screen. In the horizontal direction, the screen has a horizontal distribution, wherein the light rays generally are reflected along a predetermined illumination spread with respect to the horizontal axis.
The front projection display further may include modular and separate electronic and imaging modules. The imaging module may be placed inside the projection head and the electronic module is placed in the swiveling arm.
The electronic module may be enclosed by a honeycomb structure. A cooling fan produces a cooling air current and the honeycomb structure directs the cooling current to flow through the length of the hollow structure. The honeycomb acts as a heat exchanger and the heat generated by the projector is dissipated by convection by the cooling current. The honeycomb structure also acts as an EMI/RFI shield. The cell size, material thickness and orientation of the honeycomb structure are tuned to attenuate undesirable high electromagnetic frequencies.
In an alternative embodiment, the front projection display may include a light source remotely placed from the imaging components and a flexible illumination waveguide. The illumination waveguide then optically couples the light source to the imaging components in the projection head. Also in alternative embodiments, the front projection display system may include a CPU placed within the frame and digital annotation components.